I can pick up a new set of Enve wheels on a pretty good deal. They will go on my all-road bike. I can only get one. Would you go M50 or the new 4.5 AR?

The 4.5 seem awesome. It would give me a ton of flexibility on the single frame (basically making it a road bike with the right setup). I could use my aluminum wheels for wide tires. However, I just wonder if the tougher mountain bike oriented wheels (that can still run a 28c tire) might be the more logical choice.

Thoughts?